IRLF 


B    3 


333 


LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Ciass 


ENGINEERING  NEWS  REPRINTS  25  Centt 

The 

Preparation  of  Drawings 
and  Other  Illustrations 
for  Photo-Reproduction 


REINHARDT 


Reprinted  from  ENGINEERING  NEWS,  February  15,  1906 


Hl\n\ng 


LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Class 


r/ 


The    Preparation   of   Drawings 

and  Other  Illustrations  for 

Photo-Reproduction 


CHAS.    W.  REINHARDT 

A 
Chief  of  Drafting  Department,  Engineering  News 

Author  of  "  Technic  of  Mechanical  Drafting,"  "  Lettering  for 
Architects,  Engineers  and  Draftsmen." 


Fe§runt'y>  1 5,  1906) 


PRICE  25  CENTS 


NEW  YORK 
THE  ENGINEERING  NEWS  PUBLISHING  CO 


'*    •*•  •      •  •   • 

'  •  *     •  l  •*    •    • 

** 


The    Preparation   of  Drawings  and  Other  Illustra- 
tions for    Photo=Reproduction. 

There  is  probably  no  other  adjunct  to  the  mak- 
ing of  technical  literature  which  is  so  little  un- 
derstood and  so  carelessly  handled  as  the  prepara- 
tion of  the  necessary  text  illustrations.  And  yet 
a  great  many  publications  depend  for  their  prin- 
cipal value  upon  the  illustrations  which  accom- 
pany the  text  matter.  It  therefore  follows  that 
poorly  rendered  illustrations  will  detract  not  only 
from  the  appearance,  but  also  from  the  useful- 
ness, of  a  book  or  paper,  as  compared  with  illus- 
trations neatly  and  clearly  executed,  correctly 
drawn  as  to  details  and  legibly  lettered. 

For  the  reproduction  of  line  drawings  many 
authors  and  publishers  resort  to  the  so-called 
"wax  engraving  process."  Here  the  original, 
either  a  tracing,  or  a  blue-print,  or  pencil  sketch 
on  detail  paper,  is  photographed  in  the  desired 
size  upon  the  sensitized  waxed  surface  of  a  cop- 
per plate.  The  outlines  of  the  drawing  are  then 
scratched  through  this  wax  enamel  down  to  the 
blackened  copper  backing  by  means  of  different 
sized  gravers.  The  lettering  on  such  a  drawing 
is  set  up  in  type  and  stamped  into  the  softened 
wax.  The  finished  wax  engraving  is  "electro- 
typed,"  the  film-like  copper  covering  on  the  wax 
mold  is  backed  with  type-metal,  mounted  "type- 
high,"  and  is  then  ready  for  printing. 

The  wax  engraving  is  considered  by  numbers  of 
technical  men  as  the  very  acme  of  perfection, 
since  the  lines  print  clean  and  sharp  and  the  let- 

3 

224500 


tering  is  legible.  Such  illustrations  certainly  have 
a  smooth  and  finished  appearance,  but  they  are 
to  a  large  extent  routine  copies  of  poor  originals, 
with  more  or  less  liability  of  errors  and  omissions, 
as  every  line  must  be  ruled  in  by  hand  and  all 
the  lettering  must  be  reproduced  by  setting  type" 
and  impressing  it  in  the  wax.  Since  it  is  easier 
to  get  superficially  passable  results  from  a  poor 
drawing  by  means  of  the  wax  process  than  by 
the  processes  to  be  described  later,  there  is  per- 
haps more  likelihood  that  poor  material  for  il- 


Boiler  &  Engine  Koojm  Main  Air  Supply 
|/^_  Laundry  Floor  AvarmAir  Supply 

((Servants  Dining  Rohm  warm  Air  Supply 
|\— ^V^Heatij.s  Ajaln   W>  Exhaust 


Fig.     1.     Facsimile   Reproduction   of  "Wax- engraving. 

lustrations  will  be  used  for  the  wax  than  for  the 
other  processes.  The  clear,  even  lines  and  uni- 
form, legible  lettering  of  the  wax  engraving  cover 
a  multitude  of  sins  and  give  rise  to  many  illus- 
trations which  are  of  little  use  for  purposes  of 
careful  study.  This  is  most  likely  to  be  true  when 
the  illustrations  are  complex.  For  simple  line 
drawings  and  diagrams  the  wax  process  has  much 
to  commend  it,  especially  where  the  services  of 
good  draftsmen  are  not  available. 


When  an  author  or  publisher  wishes  to  make 
sure  of  a  facsimile  reduction  of  as  perfect  a  line 
drawing  as  is  needed  for  his  purpose,  he  will  have 
it  reproduced  by  photo-lithography  or  by  photo- 
engraving on  zinc.  Photo-lithography  is  generally 
employed  for  making  large-sized  illustrations  for 
folding  sheets  and  insets,  which  cannot  very  well 
be  handled  economically  by  the  ordinary  printing 
press.  The  originals  require  the  same  finish  as 
those  used  for  the  zinc  process.  The  photographs, 
reduced  to  the  desired  size,  are  transferred  to  a 
polished  lithographic  stone,  which,  after  being  re- 
etched,  is  ready  to  print  from  in  the  lithographic 
press.  Original  photographs  may  also  be  repro- 
duced in  this  way,  giving  the  same  general  result 
as  by  the  more  familiar  half-tone  process,  de- 
scribed further  on. 

A  line  engraving  on  zinc  is  produced  by  first 
printing  a  reversed  negative,  made  from  a  large 
original,  upon  a  polished  and  sensitized  zinc 
plate.  When  inked  by  means  of  a  printing  roller, 
the  ink  adheres  to  the  black  lines  of  the  plate, 
corresponding  to  those  on  the  original  drawing. 
Powdered  resin  is  then  sprinkled  over  the  plate. 
It  adheres  to  the  ink  lines,  and  on  being  heated 
it  melts  and  forms  a  protective  coating  against 
the  etching  solution.  This  solution  is  next  poured 
over  the  plate  and  is  allowed  to  remain  until  it 
eats  out  enough  of  the  metal  between  the  lines  to 
leave  the  latter  in  clear  relief.  More  metal  is  then 
removed  or  "routed"  from  between  the  lines  by 
means  of  a  finishing  tool.  Finally,  the  zinc  plate 
is  mounted  upon  a  wood  block  and  is  ready  for 
use  in  the  printing  press. 

The  process  thus  briefly  outlined  requires  in  the 
way  of  original  drawings  pure  black  lines  on  a 
clear  white  or  bluish-white  background.  The  me- 
dium upon  which  to  draw  may  therefore  be  white 


paper,  tracing  paper  or  transparent  vellum.  Buff 
colored  paper  has  sometimes  yielded  fair  results, 
but  its  use  is  not  advisable.  It  must  be  remem- 
bered from  the  very  outset  that  the  drawing  is 
to  be  made  for  a  certain  amount  of  reduction, 
generally  large,  and  that  consequently  it  must  be 
made  so  that  when  reduced  its  details  will  still 
be  recognizable,  its  lines  still  separated  from 
each  other,  and,  above  all,  lettering  and  descrip- 
tive symbols  must  be  readily  legible. 

The    reductions    to    which    drawings    are    sub- 
jected may  vary  all  the  way  from  "one-half"  to 


Fig.  3.     Reproduction  from  Fig.  2. 

"nine-tenths";  that  is  to  say,  from  one-half  to 
one- tenth  the  original  size  (linear  measure).  An 
easy  reduction  to  work  for  may  be  called  the 
"two-thirds"  reduction,  or  to  one-third  the  linear 
measure  of  the  original.  The  lines  in  such  a 
drawing  will  have  to  be  neither  too  bold  nor  too 
fine,  and  the  lettering  may  be  made  of  moderate 
size.  As  stated  above,  the  draftsman  must  know 
from  the  very  outset  the  rate  of  reduction  and 
must  proceed  accordingly,  always  having  in  mind, 
for  instance,  that  for  a  two-thirds  reduction  his 
lines  must  be  three  times  the  width  of  those  on 
the  final  proof  taken  from  the  finished  plate. 
This  rule,  however,  need  not  be  carried  out  rig- 
idly, because  fairly  fine,  black  lines,  having  a 
ridge  of  ink  on  top,  will  always  possess  a  value 


in  photographing,  and  will  consequently  be  re- 
corded upon  the  negative.  Some  draftsmen  are 
in  the  habit  of  screwing  up  the  nibs  of  the  ruling 
pen  tightly,  so  as  to  produce  a  fine  line.  The  re- 
sult is  that  the  ink  is  squeezed  out  beneath  the 
points  and  a  gray,  very  fine  line  will  result,  which 
will  either  not  photograph  at  all  or  come  out  only 
in  spots.  Therefore,  it  is  advisable  never  to  try 
to  introduce  too  fine  lines  into  any  drawing,  and 
it  is  necessary  to  make  sure  that  all  lines  are 
perfectly  black. 

When  working  for  reduction  a  drawing  should 
always  be  presented  in  its  essential  details;  all 
unnecessary  center-lines,  invisible  and  construc- 
tion lines,  as  well  as  dimensioning,  should  be 
omitted.  In  order  to  make  clear  the  construction 
of  whatever  object  may  have  to  be  presented,  a 
certain  amount  of  outline  shading,  very  boldly 
executed,  may  prove  of  great  value.  The  shading 
should  be  heavy  and  decisive,  the  shade-lines  be- 
ing five  or  six  times  as  heavy  as  the  ordinary 
outlines.  The  draftsman  must  be  quite  sure  In 
his  own  mind  as  to  what  parts  must  "stand  out," 
as,  also,  what  portions  should  be  shown  as  reced- 
ing, and  shade  accordingly. 

Center-lines  should  be  shown  the  strength  of 
ordinary  outlines.  The  neatest  symbol,  and  most 
suggestive  perhaps,  is  the  "dash  and  dot"  line, 
with  regular  spacing  between,  showing  dashes 
shorter  than  is  customary  at  present.  Invisible 
and  construction  lines  should  only  be  employed 
where  clearness  demands  their  use;  short  dashes 
will  answer  very  well  for  that  style  of  lines.  Di- 
mension lines  in  a  well  executed  drawing  should 
be  the  least  prominent  of  all,  and  should  there- 
fore be  shown  in  very  short  light  dashes  or  dots, 
leaving  open  spaces  for  the  dimensions  them- 
selves. In  this  way  the  solid  outlines  of  the 

I 


drawing  are  not  in  any  way  interfered  with;  the 
eye  takes  in  at  a  glance  the  object  itself;  all  aux- 
iliary lines  are  thus  made  of  secondary  impor- 
tance. 

Additional  clearness  may  at  times  be  gained  by 
introducing  a  few  touches  of  curved  surface  shad- 
ing, where  such  will  aid  the  understanding  of  a 
certain  shape,  which  perhaps  is  not  otherwise 


Fig.  4.  Reproduction  of  portion  of  drawing,  where  all 
hidden  parts  are  carefully  outlined  in  broken  lines, 
which,  nevertheless,  do  not  interfere  with  the  "visible" 
outlines.  All  unnecessary  center-lines  are  omitted. 

made  clear  by  any  other  view.  Such  shading, 
where  properly  executed,  will  greatly  improve  the 
appearance  of  a  drawing,  but  is  unfortunately 
often  used'  indiscriminately,  and  in  such  cases 
detracts  from  the  clearness  of  the  illustration.  In 
the  style  of  shading  there  is  a  special  tendency 
for  the  draftsman  to  use  too  close  a  spacing. 
Where  portions  of  a  view  are  to  appear  in  sec- 
tion, the  proper  section-lining  should  conscienti- 

9 


ously  be  used,  being  quite  sure  that  all  such  . 
parts  are  properly  designated  in  this  way.  Parts 
shown  in  elevation  should  under  no  circumstances 
receive  any  such  ruling;  a  very  rigid  distinction 
should  always  be  made  between  parts  in  section 
and  parts  in  elevation  by  the  use  of  correct  sec- 
tioning in  the  former  only. 

The  lettering  of  a  drawing  which  has  been  fin- 
ished up  to  that  point  must  again  be  put  in  with 
a  view  of  purely  supplementing  the  drawing,  and 
perhaps  the  accompanying  text  matter.  It  should 
all  be  placed  so  that  it  may  be  read  from  the 
base  and  the  right-hand  side  of  the  sheet.  A 
proper  distribution  of  such  descriptive  matter  in 
the  shape  of  notations,  titles  and  numerals  will 
wonderfully  enhance  the  appearance  of  a  drawing 
—the  reverse  also  holds  good.  There  should  be  no 
attempt  to  crowd  dimensions,  reference  letters  or 
small  notes  into  their  respective  spaces  where 
such  are  too  small.  Instead,  they  should  be 
placed  boldly  outside  or  opposite,  as  the  case  may 
be,  and  dotted  reference  lines  used,  with  arrow- 
heads attached.  This  rule  should  be  adhered  to 
especially  where  there  is  no  great  amount  of  let- 
tering used,  so  that  in  such  a  case  the  outlines  of 
the  figures  are  permitted  to  stand  out  clearly 
and  distinctly  by  themselves.  The  style  of  let- 
tering used  depends,  of  course,  greatly  upon  usage 
and  individual  preference;  but  no  lettering  for 
reduction  work  can  compare  in  legibility  and  ra- 
pidity of  execution  with  the  so-called  one-stroke 
Gothic  lettering,  either  inclined  or  vertical.  The 
inclined  style  can  with  advantage  be  used  for  all 
purely  descriptive  matter,  dimensions,  notations, 
etc.;  the  upright  lettering  will  naturally  commend 
itself  for  sub-captions,  reference  letters  and  main 
divisions,  which  ought  to  be  emphasized.  The  so- 
called  "all-cap"  lettering  requires  more  time  to 

10 


construct,  and  is  not  so  readily  legible  as  the 
"cap-and-lower-case"  lettering1,  which  latter  style 
has  for  those  reasons  come  into  almost  universal 
favor.  Main  titles  or  captions  for  any  reproduc- 
tion can  cheaply  and  neatly  be  set  up  in  type; 
therefore  the  construction  of  such  by  hand  on 
any  drawing1  for  photo-reproduction  is  nearly  al- 
ways useless  and  expensive.  Underlining  of  let- 
tering is  undesirable,  as  it  tends  to  distract  at- 
tention from  the  outlines  of  the  drawing  itself. 
As  the  one-stroke  lettering  is  supposed  to  be 
drawn  in  uniform  strength  of  body,  a  specific 
mode  of  procedure  becomes  necessary— the  direc- 
tion of  strokes  and  their  sequence  ought  to  be 
carefully  studied  by  every  draftsman. 

The  different  reductions  to  which  a  drawing 
may  have  to  be  subjected  require,  of  course,  dif- 
ferent sizes  of  lettering,  and  well  worn  pens  of 
different  makes  can  be  used  to  produce  just  the 
requisite  strength  of  body  for  the  letters,  with  one 
application  for  each  stroke,  for  it  goes  without 
saying  that  the  strength  of  the  body  of  the  let- 
ters must  be  in  accordance  with  their  respective 
sizes.  For  lettering  on  a  drawing  above  a  "five- 
sixths"  reduction  (i.  e.,  to  be  reduced  to  one-sixth 
its  original  length),  a  stiff,  red  sable  brush  can 
be  used  with  advantage.  In  order  to  be  legible  to 
the  average  reader,  the  lettering  on  any  reproduc- 
tion should  not  come  out  smaller  than  uniformly 
one  millimeter  high  in  the  small  lower-case  let- 
ters, such  as  "a,"  "e,"  "m,"  "n,"  for  instance. 
The  other  letters  must,  of  course,  show  in  pro- 
portion. Therefore  the  lettering  on  an  original, 
which,  for  example,  is  to  be  reduced  three-fourths 
(i.  e.,  one-fourth  its  present  length)  must  be  made 
in  the  small  lower-case  letters  mentioned  four 
millimeters  high,  with  strength  of  body  in  pro- 
portion. A  drawing  thus  lettered  up  and  exe- 

11 


K~. 


cuted  will,  of  course,  stand  a  much  greater  reduc- 
tion and  yet  show  legible  and  clear;  neverthe- 
less, the  standards  given  here  have  been  followed 
where  absolutely  good  work  has  been  essential. 
Corrections  and  erasures  should  be  very  carefully 
made,  as  the  brownish  tint  so  often  noticeable 
on  tracing-cloth  where  erasures  have  occurred 
will  show  on  the  negative  obtained  by  photograph- 
ing, and  must  be  attended  to  separately.  Such 
places  can  be  covered  up  by  painting  Chinese 
white  over  the  spots  affected. 

Very  often  the  reproductions  are  overloaded 
with  non-essential  details,  every  center-line  being 
shown,  the  dimension  lines  all  ruled  in  solid,  and 
a  mass  of  almost  illegible  lettering  being  spread 


Fig.  6.     Reproduction  from  Fig.  5. 

over  the  whole  illustration.  The  reader  of  such 
illustration  is  put  to  considerable  trouble  to  in- 
terpret the  drawing;  he  has  to  make  his  own 
deductions,  read  between  the  lines,  as  it  were, 
and  often  gives  up  the  task  in  disgust.  All  this 
is  caused  by  reproducing  an  unsuitably  drawn 
and  lettered  illustration,  almost  useless,  at  the 
best;  certainly  not  serving  as  an  ornament  to  the 
publication  in  which  it  appears. 

There  is  no  reason  why  many  original  drawings 
cannot  be  made  so  bold,  in  both  lines  and  letters, 
that  instead  of  having  the  originals  blue-printed 
in  the  ordinary  cumbersome  way  they  could  sim- 
ply be  photographed  down  to  perhaps  one-fourth 
their  length.  Portfolios  containing  such  reduced 
original  drawings  of  the  Pittsburg  Filtration 

13 


Works  and  of  the  recent  improvement  of  the  New 
York  Central  R.  R.  appear  exceedingly  handy 
and  serviceable,  and  are  certainly  far  superior  to 
the  unwieldy  and  at  times  almost  unmanageable 
roll  of  blue-prints,  which  otherwise  have  to  be 
handled. 

It  may  be  mentioned  as  a  curiosity  that  some- 
times pencil-drawings  on  tracing  paper  have 
given  good  results  in  reproduction;  the  pencil 


Fig.  7. 


Facsimile  Reproduction  from  original  unsuitably 
drawn  and  lettered. 


lines  were  evidently  black  enough  to  possess  some 
value  in  the  exposure. 

Occasionally  it  becomes  necessary  to  reproduce 
an  illustration  taken  directly  from  some  book, 
pamphlet  or  periodical.  Such  a  reproduction  can, 
of  course,  not  be  reduced  very  much,  and  from 
the  outset  of  such  operation  it  must  be  deter- 
mined just  how  much  reduction  it  can  "stand." 
The  outlines  of  the  illustration  to  be  reproduced 
can  with  some  care  be  retouched  where  ragged 

14 


or   broken.     The   principal   part    to   be   amended, 
though,    on   such   a  sheet   is   the  lettering,  which 


.-5x5  Cross  Arm 


Fig.  8.  Reproduction;  upper  portion  remodeled  for 
further  reduction;  lower  part  left  untouched  so  as  to 
show  difference  in  appearances. 

as  a  rule  is  poorly  done  and  much  too  small.  Such 
portions  of  the  lettering  as  are  essential  can  be 
pasted  over  with  slips  of  white  paper  and  the 


parts  re-lettered  to  the  right  size  upon  the  paper; 
the  portions  not  wanted  may  be  obliterated  by 
simply  painting  over  with  Chinese  white.  The  di 
mension  lines,  which  generally  were  drawn  as 
solid  lines,  can  be  cut  up  with  a  brush  or  a  fine  pen 
dipped  into  a  solution  of  Chinese  white,  so  as  to 
produce  dotted  lines  to  designate  dimensions.  The 
center  lines,  likewise,  can  be  cut  up  into  regu- 
larly spaced,  small  dots  and  dashes;  the  invisible 
or  construction  lines  can  either  be  painted  out 
altogether  or  similarly  treated.  Where  outline 
shading  is  absent  on  reproductions,  such  shading 
may  sometimes  be  added,  if  the  paper  possesses  a 
fairly  good  surface.  Such  a  remodeled  drawing 
shows  up  very  well  in  the  proper  reduction,  and 
can  be  made  fully  as  serviceable  for  purposes  of 
study  as  a  well-executed  original  drawing. 

The  principles  of  the  so-called  "half-tone  pro- 
cess" are  similar  to  those  governing  the  making 
of  line-engravings,  with  the  exception  that  the 
original,  consisting  either  of  wash-drawing  or  a 
photograph,  is  photographed  through  a  screen.  The 
impression  recorded  on  the  sensitized  plate  there- 
by is  a  number  of  opaque  dots  of  varying  size, 
the  white  sections  of  the  original  assuming  the 
largest  size,  the  dots  growing  smaller  in  the 
darker  portion  until  they  are  completely  lost  in 
the  solid  blacks.  The  effect  is  a  picture  in  dots, 
the  varying  shades  and  tints  being  depicted  by 
various  sized  dots. 

The  impression  from  the  reversed  negative  is 
taken  upon  a  highly  polished,  sensitized  copper 
plate,  which,  after  repeated  etchings,  is  ready  for 
the  wood  mounting.  The  finishing  of  such  a  plate 
consists  in  local  re-etching,  a  procedure  which  will 
diminish  the  size  of  the  dots  in  places,  making 
them  print  lighter  in  the  finished  picture.  At  times 
the  dark  or  black  portions  may  have  to  be  "pol- 

10 


ished"  in,  the  fine  white  dots  in  such  places  there- 
by being  obliterated,  so  that  these  portions  will 
print  perfectly  black.  Where  repeated  local  re- 
etching  fails  to  do  justice  to  the  high  lights  shown 
in  the  original,  such  parts  may  boldly  be  en- 
graved out  by  a  skillful  finisher,  so  that  the: 
may  print  absolutely  clear  white. 
If  a  highly  finished  picture  is  wanted,  exhibit- 


Fig.  9.  Specimen  of  retouched  half-tone;  coast  in  dis- 
tance is  accentuated  purely  by  outlines;  steel  pier 
in  intermediate  distance  is  also  strengthened  by  light 
outlines,  whereas  foliage  in  foreground  received  the 
highest  lights  and  deepest  shadows. 

ing  high  lights  and  deep  shadows,  or  where  the 
judgment  of  the  finisher  is  not  exactly  trusted, 
resort  must  be  had  to  retouching  the  original 
photograph.  On  the  ordinary  brown  or  solio 
prints  the  high  lights  are  painted  in  with  pure 
Chinese  white,  or  the  same  mixed  with  vermillion, 
so  as  to  somewhat  match  the  tone  of  the  pho- 
tograph. Deep  shadows  are  produced  by  lamp- 
black with  a  trifle  of  vermillion  added.  Solid 

17 


blacks  can  be  effected  by  the  use  of  India  ink. 
The  purpose  arrived  at  in  all  cases  is,  of  course, 
to  somewhat  exaggerate  the  contrasts,  as  the 
interposition  of  the  screen  in  photographing  the 
original  will  have  a  tendency  to  reduce  values 
and  more  or  less  flatten  the  tints.  At  times  the 
contours  of  an  object  shown  may  be  so  shadowy 
against  the  background  that  a  little  outlining  in 
a  light  neutral  color  may  be  all  that  is  required. 
Such  outline  may  sometimes  be  done  effectively 


Fig.  10.    Shows  original  of  Fig.  9  un-retouched. 

in  a  slightly  lighter  color,  where  dark  surfaces 
adjoin.  Nowadays  some  beautiful  work  is  being 
done  by  professional  retouchers  with  the  aid  of 
the  air-brush,  which  is  worked  by  compressed 
air.  The  illustrations  for  modern  trade  cata- 
logues, with  their  magnificent  cloud  backgrounds, 
are  nearly  all  prepared  by  means  of  the  air- 
brush. 

Most  photographs  will  be  found  to  have  a  glazed 
or  polished  surface,  which  will  not  receive  water 
colors  readily.  In  such  cases  the  surface  can  be 

18 


gone  over  gently  with  an  ordinary  artist's  rubber, 
taking  care  not  to  cause  any  streaks  or  scratches. 
At  times  some  rubbing  with  the  tip  of  the  finger 
to  which  a  little  powdered  pumice  has  been  ap- 
plied, may  be  effective  upon  refractory  portions. 

Retouching  of  "Velox"  prints  can  be  done 
with  neutral  colors  without  any  admixture  of 
vermillion  or  brown.  Here  the  black  generally 
needs  reinforcing.  On  dull  Velox  prints  some  good 


Fig.    11.      Reproduction   from    half-tone;    screen    does   not 

match  properly. 

work   can    sometimes   be   done   with    an   ordinary 
H.  B.  drawing  pencil. 

As  occasionally  reproductions  from  line-engrav- 
ing can  effectively  be  "doctored  up,"  so  also  proofs 
from  half-tones  may  be  prepared  for  a  new  re- 
production. The  proofs  cut  from  magazines  or 
trade-papers  can  be  mounted,  and  where  judi- 
ciously  retouched  will  give  very  good  results 
The  only  difficulty  which  engravers  generally  en- 
counter in  this  class  of  work  is  the  matching  of 
their  screen  upon  the  screen  which  the  original 
contains.  If  this  cannot  be  done  correctly  a  pe- 
culiarly mottled  effect  upon  the  surface  of  the 
new  plate  will  result. 

19 


At  times  it  may  become  desirable,  for  one  pur- 
pose or  another,  to  entirely  redraw  an  unsatis- 
factory small  illustration,  or  to  make  a  pen-and- 
ink  sketch  from  a  photograph.  In  such  a  case 
a  "silver-print"  enlargement  is  made  from  the 
original;  the  silver-print  is  mounted  and  Is  ready 
for  drawing.  The  light-brown  tint  of  such  apHnt 
permits  of  distinguishing  the  lines  drawn  upon  It; 
only  the  absolutely  necessary  outlines  should  be 
drawn  upon  the  print  with  waterproof  ink;  parts 
which  ought  to  be  amended  or  points  to  be  pre- 
served and  nevertheless  to  be  modified  in  execu- 
tion can  be  drawn  on  in  pencil.  After  this  has 
been  done  the  print  is  bleached  in  an  enameled 
pan  with  a  bichloride  of  mercury  solution,  the  ap 
plication  of  which  will  cause  the  photographic  color 
to  disappear,  leaving  only  the  pure  white  paper, 
with  black  ink,  or  occasional  pencil  outlines  upon 
it.  After  rinsing  in  clean  water  the  print  is 
ready  to  continue  with  when  dry.  Such  a  draw- 
ing can  be  finished  in  the  style  advocated  above; 
a  pen-and-ink  sketch  can  be  executed  purely  in 
black  and  white,  following  the  technic  observed 
in  an  etching,  or  a  newspaper  illustration.  Small 
mistakes  can  be  rectified  by  painting  over  with 
Chinese  white.  A  good  rule  to  follow  is  to  draw 
general  outlines  on  such  prints  sufficiently  heavy, 
as  the  reflection  of  the  pure  white  background 
upon  the  black  lines  will  have  a  tendency  to 
make  them  appear  too  narrow  in  photographing. 
As  a  rule,  all  pen-and-ink  portraits  for  periodicals 
are  made  in  this  manner.  A  drawing  upon  a 
bleached  silver-print  should  never  be  exposed  very 
long  to  bright  light,  as  otherwise  the  original 
brownish  tint  of  the  print  will  begin  to  reappear, 
a  matter  which  would  make  a  good  photo-repro- 
duction of  the  drawing-  impossible. 


I'O 


ENGINEERING  NEWS  REPRINTS 

A  Series  of  Reprints  of  some  Articles  of  more 
permanent  value  in  Technical  Work  that 
have  appeared  in  ENGINEERING  NEWS.  :: 

UNIFORM  SIZE:   4^x7  Ins.;  FLEXIBLE  PAPER  BINDING 
PRICE,  25  CENTS  EACH 

No.  I.  Ignitions  and  Explosions  in  the  Discharge  Pipes 
and  Receivers  of  Air  Compressors.  By  ALEX.  M. 
Gow,  M.  E.  20  pages,  one  page  diagram. 

No.  2.  The  Structural  Design  of  Towers  for  Electric 
Power-Transmission  Lines.  By  JOSEPH  MATEB. 
M.  Am.  Soc.  C.  E.  27  pages,  3  illustrations. 

No.  3.  The  Design  of  High  Abutments.  By  WM.  11. 
TOBBANCE.  M.  W.  8.  E.  13  pages,  12  figs,  (includ- 
ing folding  plates). 

No.  4.  The  Preparation  of  Drawings  and  Other  Illustrations 
for  Photo-Beproduction.  By  CHAS.  W.  KEINHABDT, 
Chief  Draftsman,  Engineering  News.  20  pages,  11  illus- 
trations. 


